Broadband telecommunications, such as broadband ISDN and motion video (e.g., television broadcast) communications, operate at very high transmission rates, typically at tens or hundreds of megahertz. To switch such telecommunications, switching systems are required that are capable of operating at corresponding or higher rates. Conventionally, bandwidth-division switching systems such as space-division and wavelength-division switching systems have been used for this purpose. However, conspicuously absent has been the use of time-division switching systems for such applications. The reason is that time-division multiplexing increases the rate at which the switch must operate, by a multiple of an individual switched communication's transmission rate. Hence, time-division switching systems operating at hundreds of megahertz or even gigahertz are required to switch broadband telecommunications.
Recently, time-division switching systems capable of operating at these very high rates have become feasible. In their simplest form, such switching systems consist of a time-multiplexed switch (TMS) stage that has incoming time-division multiplexed (TDM) telecommunication links coupled thereto through a time-slot interchange (TSI) stage. Unfortunately, time-slot interchangers capable of operating at hundred-megahertz or gigahertz rates are very expensive, to the extent that the cost of the TSI stage dwarfs the cost of the TMS stage and makes the whole switching system prohibitively expensive. Hence, while time-division switching systems capable of handling broadband telecommunications have become technically feasible, they have yet to become commercially practical.